Superconductivity in Hourglass Dirac Chain Metals (Ti, Hf)IrGe

Realizing superconductivity in stoichiometric topological materials is a major focus in condensed matter physics, as it paves the way to achieve topological superconductivity. Here, it is reported that the discovery of ternary germanide superconductors, MIrGe (M = Ti, Hf), predicted to exhibit non-symmorphic symmetry-protected hourglass Dirac chains, can be prime candidates for topological superconductivity. Using comprehensive thermodynamic and muon-spin rotation/relaxation (µSR) measurements, these materials are established as conventional bulk type-II superconductors with transition temperatures of 2.24(5) K for TiIrGe and 5.64(4) K for HfIrGe, featuring a full gap and preserved time-reversal symmetry. First-principles calculations reveal striking topological features in MIrGe, including hourglass-shaped bulk dispersions and a Dirac chain - a ring of fourfold - degenerate Dirac points protected by nonsymmorphic symmetry. Each Dirac point corresponds to the neck of the hourglass dispersion, while the Dirac chain gives rise to drumhead - like surface states near the Fermi level. Additionally, nontrivial $Z_2$ topology leads to isolated Dirac surface states with helical spin textures that disperse across the Fermi level, forming an ideal platform for proximity-induced topological superconductivity. The coexistence of conventional bulk superconductivity, symmetry-protected hourglass topology, and helical spin-textured surface states suggests MIrGe as a rare platform to achieve topological superconductivity, opening new avenues for next-generation quantum technologies.